Severing brittle flat materials such as glass, sapphire, silicon, gallium arsenide or ceramics by producing a notch along the desired dividing line, along which breaking stresses are subsequently produced by subjection to mechanical forces, which leads to the complete separation of the flat material, is already known.
In order to sever the flat material in this way, the depth of the notch must be at least one-third of the flat material thickness. The notch can be applied mechanically or by means of lasers. Particularly for dicing chips from substrates (wafers), laser methods that create a notch by ablation into the material are increasingly being used. The notches are typically only a few μm wide and have an approximate depth of ⅓ the flat material thickness. The notch depth is produced proportionately to the total thickness of the flat material, depending on its brittleness. It is disadvantageous that every volume of removed material potentially contributes to the microscopic contamination of the material being processed. Since the aspect ratio between notch width and notch depth is critical to all these laser processes, complex apparatuses are needed and the notch is created relatively slowly. Deep notches for thick wafers therefore require increasingly more process time.
Such methods are disclosed in US 20050153525 or US 20040228004, for example, the contents of each of which are hereby incorporated by reference in their entirety. After production of the notches, the wafer is completely severed by applying mechanical (impulse) energy or forces, for example tensile force (stretching of films), bending forces (breaking over ridges) or a combination thereof.
Mechanical application of breaking forces is geometrically relatively imprecise. Therefore fracture flaws can occur if the breakage lines do not run perpendicular to the material thickness or if two breakage lines intersecting at one point do not meet one another at the intended angle. Particularly in chip production, such breaking faults lead to a reduction of yield and must therefore be avoided. In addition, material particles split off, which can entail a macroscopic contamination of the surface of the flat material.
Instead of severing a flat material by material removal, e.g., in form of a notch as described, a known method is to produce a mechanically-induced initial crack, which is subsequently propagated through the flat material by means of thermally-induced mechanical stresses. Such a method (thermal laser separation—TLS) is described in WO 93/20015 the contents of which is hereby incorporated by reference in its entirety. It is disadvantageous particularly if a flat material separated into several parallel strips is to be severed in a second direction, for example, orthogonally to the first separation direction, for example, into individual rectangles in the dicing of a wafer into individual chips. Since a new initial crack must be made at the beginning of each dividing line in the first separation direction, the process is very time-consuming and the mechanical scoring system is subject to high wear.
The problem, which is solved by the present invention is to find a method with which brittle flat materials can be separated into a plurality of single components, in particular, with which wafers can be diced into chips, with good time efficiency and high edge quality.
This problem is solved by a method according to claim 1.
Advantageous embodiments are described in the dependent claims.